Effects of tillage, fallow and burning on selected properties and fertility status of Andosols in the Mounts Bambouto, West Cameroon

doi:10.4236/as.2011.23044

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Vol.2, No.3, 334-340 (2011)

doi:10.4236/as.2011.23044

Agricultural Scienc es

Effects of tillage, fallow and burning on selected

properties and fertility status of Andosols in the Mounts

Bambouto, W est Cameroon

Paul Tematio1*, Ertine Isabelle Tsafack2, Lucas Kengni2

1Department of Earth Science, University of Dschang, Dschang, Cameroon; *Corresponding Author: [email protected]

2Department of Earth Science, University of Dschang, Dschang, Cameroon.

Received 28 January 2011; revised 23 May 2011; accepted 7 July 2011.

ABSTRACT

To assess the imp act of land u se on the Andosol

fertility, changes in chemical and physical pro-

perties affecting soil quality were monitored on

Andosols from Mount Bambouto submitted to

four different land uses and management sys-

tems: natural cover, tillage, burning and fallow.

In comparison with the natural cover, tillage

reduces Andosol OC (6.5% to 4.8%), total N

(4.51‰ to 2.95‰), CEC (22.0 to 20.9 cmol·kg–1)

and the abundance of soil macro-aggregates

expressed by the water stable aggregates (WSA)

varies from 53.8% to 12.0%; and increases the

bulk density (0.69 to 1.09 g·cm–3) and the sum of

exchangeable cations (3.58 to 4.84 cmol·kg–1).

Burning also reduces Andosol OC (6.5% to

0.8%), total N (4.51‰ to 0.95‰) and CEC (22.0 to

10.2 cmol·kg–1), but increases soil pH (4.62 to

6.54), the sum of exchangeable cations (3.58 to

5.74 cmol·kg–1) and the abundance of soil

macro-aggregates (WSA: 38.2% to 57.0%). In

comparison with tillage, fallow increases An-

dosol OC (4.8% to 6.5%), total N (2.95‰ to

5.04‰), CEC (18.0 to 21.6 cmol·kg–1), the sum of

exchangeable cations (3.58 to 5.05 cmol·kg–1)

and the abundance of soil macro-aggregates

(WSA: 12.0% to 48.8%). Globally, the tillage man-

agement deteriorates Andosol chemical and

physical properties affecting fertility, whereas

the fallow management restores them. The

burning management also improves some An-

dosol chemical and physical properties affect-

ing quality, but it won’t last long.

Keywords: Andosols; Land Use Management

Systems; Soil Physic-Chemical Properties; Soil

Fertility

1. INTRODUCTION

Soil quality is fundamental for sustainable agriculture

development [1]. The land use and management systems

strongly influence soil quality expressed by changes in

soil chemical and physical properties (organic matter

content, CEC, sum of exchangeable cations, acidity, bulk

density, aggregates stability, etc.). Thus, improper land

use and management systems reduce soil fertility and the

subsequent food security [2]. Many studies on soil fertil-

ity have focused mainly on nutrients budget and bal-

ances [3,4] without emphasis on changes in soil chemi-

cal and physical properties affecting soil quality over

time.

In Mount Bambouto, a volcanic mountain of the West

Cameroon Highlands where Andosols are widespread [5]

(Figure 1), strong human pressures on lands expressed

by the tillage and burning management systems have

affected the agro-ecosystems over the past 30 years [6].

One of the consequences is the overexploitation of soil

resources with subsequent crop yields decrease. Consid-

ering the precarious conditions of Andosols character-

ized by a rapid degradation of the majority of their

chemical and physical properties when farming, new

strategies for sustainable management of Andosols in

this area have to be found urgently. Therefore, it might

be useful to identify the land use and management sys-

tems impacts on Andosol fertility in Mount Bambouto.

The main objective of this study is to quantify changes

in chemical and physical properties of the Andosols from

Mount Bambouto submitted to tillage, burning or fallow

management systems in order to compare the effects of

these land uses and management systems on Andosol

quality changes. This would contribute to propose stan-

dard systems that safeguard Andosol quality.

2. MATERIALS AND METHODS

This study was carried out in Mount Bambouto, one

P. Tematio et al. / Agricultural Science 2 (2011) 334-340

335335

Figure 1. Location of the studied plots in the soil distribution

map of Mount Bambouto (after Tematio et al., 2004).

of the major volcanoes in the Cameroon Volcanic Line

that crosses the western part of the Cameroon territory.

In this mountain, a recent soils survey [5] points out that

Andosols are widespread above the altitude 2000 m

(Figure 1).

They are shallow weathered pedons, either with A and

BC horizons when developed on crests and steep slopes,

or A, B and BC horizons when developed on foot-slopes.

The surface horizon A is the main agricultural soil hori-

zon supporting crops farming. It corresponds to a thick

(up to 60 cm) and dark grey to dark brown (10YR3/2 -

10YR3/3) loamy soil with fine to coarse crumbly struc-

ture. These Andosols in Mount Bambouto are mainly

devoted to Irish potato and cabbage farming.

In this area, 17 plots were selected with respect to the

farming crops (Irish potatoes), the slopes gradient (slightly

undulated landscape), the landscape position (foot-slopes),

the type of land use and management system applied and

its duration. They are distributed as follow: 3 plots under

the natural cover named NT, 2 plots under the short-term

(5 years) tillage (T1), 4 plots under the long-term (10

years) tillage (T2), 2 plots under the short-term (5 years)

burning (B1), 2 plots under the long-term (10 years)

burning (B2), 2 plots under the short-term (5 years) fal-

low (F1) and 2 plots under the long-term (10 years) fal-

low (F2). In this area, the most significant variations in

chemical and physical properties induced by the different

land use and management systems occurred within the

first 40 cm of the surface horizon A. That is why in each

selected plot, soil samples for chemical analyses were

collected at 20 cm depth, mixed, air dried, crushed and 2

mm sieved. Undisturbed soil samples were also collected

at the same depth for bulk density and aggregates stability

measurements.

Chemical analyses include the soil organic carbon

(OC), the total nitrogen (N), the available phosphorus

(P), the exchangeable cations; the cations exchange ca-

pacity (CEC) and the soil pH. OC was extracted by oxi-

dation with potassium dichromate in strongly acid solu-

tion and determined using a TOC-5000A analyzer. The

total N was determined by Kjeldahl method, the avail-

able P by Bray II method and the exchangeable cations

extracted by NH4OAc buffered at pH 7 and determined

by atomic absorption spectrophotometer. The CEC at pH

7 was determined using ammonium acetate method. The

soil pH was determined in a 1:2.5 soil suspension with

deionised water.

Physical analyses refer to the bulk density (da), the

particle size distribution and the soil aggregate stability.

da was obtained using the cylinder of Koppeki method

[7]. With regard to the particle size distribution, sand

fraction was separated by wet-sieving with 63 µm sieve,

oven dried at 105˚C and weighed. Silts and clay frac-

tions were determined by laser diffraction after destruc-

tion of organic matter with hydrogen peroxide, followed

by the particle dispersal in sodium hexametaphosphate

solution. The soil aggregate stability was determined

according to Le Bissonnais method [8] which combines

3 disruptive tests: slow wetting, fast wetting and me-

chanical breakdown by shaking after pre-wetting tests.

After each test, residual aggregates were collected and

sieved using a column of six sieves: 2000, 1000, 500,

200, 100, and 50 μm. The proportion of each fraction

size of stable aggregates was calculated.

Data analyses refer to the sum of exchangeable cations

(S), the cations equilibrium (Ca/Mg/K), Al3+ toxicity (m)

and the soil aggregate stability calculation. S is obtained

by summing up the exchangeable cations. The cations

equilibrium noted (Ca/Mg/K) is the relative abundance

of Ca2+, Mg2+ and K+ in soil qualifying the competition

between the above cations during plant nutrition.



mAl



 . (1)

represents the concentration of free Al3+ in the soil solu-

tion. The soil aggregate stability is expressed by the wa-

ter stable aggregates (WSA), the geometric mean diame-

ter (GMD) and the mean weight diameter (MWD) of the

soil aggregates above 0.5 mm size. They correspond to:

iwx

WSA w



. (2)

log

exp

GMD w





. (3)

P. Tematio et al . / Agricultural Science 2 (2011) 334-340

336

Table 1. Mean values of the physical and chemical soil characteristics in the study plots.

Soil organic matter Exchangeable cations Exchange-

able acidity

Soil

acidity

Particles size

distribution (%)

Study

plots OC (%) N (‰(mg·kg–1) (cmol·kg–1)

Bulk

e Coarse sand

Cations

equilib-

rium

(Ca/Mg/K)

) P Ca2+ Mg2+ K

+ Na+ S

CEC

Al3+ m (%)pH

density

(g·cm–3) clay Fin

silt silt (76/18/6)

Not

tilled NT 6.5 ± 1. 1.0 1.68 0..58 ±

0.4

22.0 ±29 04 4.51 ± 1.1 7.0 ± 94 0.76 0.03 33.1 0.31 5.9 ±

1.7 4.62 ±

0.2 0.69 .0 52.0 17.0 2.78/17/5

T1 3.±

0.7 18.0

± 1.9 31.0 4.

0.5 0.93

low

5.7 ± 0.2 4.15 ± 0.6 22.2 ± 1.6 1.76 1.05 0.75 0.02 58 0.2 7.0 ± 42 ±36.0 47.0 13.0 4.054/39/7

Tilled

T2 4.8 ± 0.5 2.95 ± 0.7 11.7 ± 1.9 3.08 1.48 1.03 0.02 4.84 ±

1.1 20.9

2.7 0.19 5.5 ±

0.4 4.53 ±

0.2 1.09 31.0 53.0 13.0 3.073/20/7

B1 0.8 ± 0.0 0.95 ± 0.0 18.7 ± 0.0 6.27 4.43 3.98 0.03 5.74 ±

0.0 10.2

± 0.0 0.00 0.0 ±

0.0 6.54 ±

0.0 0.77 20.0 34.0 34.0 12.058/25/17

Burn

B2 1.5 ± 0.0 1.96 ± 0.0 43.6 ± 0.0 5.87 3.05 .3.6 0.06 3.94 ±

0.0 11.4 ±

0.0 0.01 0.1 ±

0.0 6.18 ±

0.0 0.79 14.0 49.0 29.0 2.041/51/8

F1 6.5 ± 0.2 5.04 ± 0.6 10.8 ± 0.6 2.72 1.22 0.95 0.02 5.05 ±

1.1 20.6

± 1.0 0.27 5.1 ±

3.1 4.64 ±

0.1 1.14 25.0 45.0 28.0 2.078/17/5

Fal-

F2 5.5 ± 0.3 1.87 ±

0.3 15.9 ± 0.8 1.67 1.06 1.01 0.01 4.39 ±

0.0 21.6

3.2 0.31 5.7 ±

1.1 4.47 ±

0.00 1.09 31.0 50.0 16.0 3.063/33/4

Openly accessible at

WD xw



. 4

here n is the number of aggregate size ranges above

0.5 mm, wi is the weight of aggregates in a size class of

average diameter xi, and w0 is the t

arbon (O C), Total Nitrogen (N)

study plots and

. Caange Capacity (CEC),

cle io

The CEC content is relatively high in the study plots and

0 cmol·kg) and T2 (20.7 cmol·kg), and se-

l·kg–1),

but innd F2

() 3.1.2 tions

han Exch

geabEx Catns and Acidity

otal weight of aggre-

gates placed on 5 mm sieve for analysis.

The mean values of the soil chemical and physical

properties in each series of plots under the same land use

and management system were obtained using M.S. EX-

CEL software.

3. RESULTS

3.1. Soil Chemical Properties

3.1.1. Organic C

and Available Phosphorous (P)

The soil OC content is high in the

varies from 4.8% to 6.5%, except in B1 (0.8%) and B

(1.5%) (Table 1). It decreeses slightly from NT (6.5%) t

(5.7%) and T2 (4.8%), and abruptly in B1 (0.8%) and

B2 (1.5%). Inversely, it increases in F1 (6.5%) and F2

(5.5%) compared to T1 and T2. The total N content fol-

lows the same trend like the soil OC content and varies

from 0.95‰ to 5.04‰. It thus decreases slightly from NT

(4.51‰) to T1 (4.15‰) and T2 (2.96‰), and abruptly in

B1 (0.95‰) and B2 (1.96‰), and increases significantly

in F1 (5.04‰), even remains low in F2 (1.87‰). The

available P content varies from 7.0 to 43.6 mg·kg–1 in the

study plots. Its lowest value is in NT (7.0mg.kg-1). It

increases in T1 (22.2 mg·kg–1), T2 (11.7 mg·kg–1), B1

(18.7 mg·kg–1) and B2 (43.6 mg·kg–1), but decreases in

F1 (10.8 mg·kg–1) and F2 (15.9 mg·kg–1) relative to T1

and T2.

varies from 10.2 to 22.0 cmol·kg–1 (Ta ble 1). The high-

est value is in NT (22.0 cmol·kg–1). It decreases slightly

in T1 (18.–1–1

verely in B1 (10.2 cmol·kg–1) and B2 (11.4 cmo

creases slightly in F1 (20.6 cmol·kg–1) a

(21.6 cmol·kg–1) with respects to T1 and T2. The sum of

exchangeable cations (S) is very low in the study soils

(3.6 to 5.7 cmol·kg–1). It increases slightly from NT (3.6

cmol·kg–1) to T2 (4.9 cmol·kg–1), B1 (5.7 cmol·kg–1), B2

(3.9 cmol·kg–1), F1 (5.1 cmol·kg–1) and F2 (4.3

cmol·kg–1), and remain unchanged in T1 (3.6 cmol·kg–1).

It highest content is in B1. The most abundant ex-

changeable cation is Ca2+ (1.60 to 3.92 cmol·kg–1), fol-

lowed by Mg2+ (0.61 to 2.00 cmol·kg–1), K+ (0.15 to 0.99

cmol·kg–1) and Na+ (0.03 to 0.09 cmol·kg–1). The cations

equilibrium is close to the optimal equilibrium (76/18/6)

in NT (78/17/5), T2 (73/20/7) and F1 (78/17/5), and

highly unbalanced in T1 (54/39/7), B1 (58/25/17), B2

(41/51/8) and F2 (63/33/4) with respect to a Ca defi-

ciency. The exchangeable Al3+ content varies from 0.00

to 0.28 cmol·kg–1. Consequently, the aluminium toxicity

is relatively low (m: 0.0% to 7.0%). Nevertheless, the

study soils are strongly acids (pH 4.42 to 4.64), except

for B1 and B2 with weak acid soils (pH 6.54 and 6.18

respectively). This acidity increases slightly from NT

(pH 4.62) to T1 (pH 4.42) and T2 (pH 4.53), but de-

creases abruptly in B1 (pH 6.54) and B2 (pH 6.18) and

slightly in F1 (pH 4.64) and F2 (pH 4.47) relative to T1

and T2.

P. Tematio et al . / Agricultural Science 2 (2011) 334-340

337337

r sta

Fast wetting test Stirring after wetting test

Ta b le 2. Soil aggregates stability in the study plots (WSA: wateble aggregates; GMD: geometric mean diameter; MWD: mean

weight diameter).

Slow wetting test Test

Study plots WSA (%)GMD (mm) MWD (mm)WSA (%)GMD (mm)MWD (mm)WSA (%) GMD (mm)MWD (mm)

Not tilled NT 53.8 1.76 2.69 38.9 1.55 1.95 38.2 1.47 1.91

T1 48.4 1.62 2.42 37.9 1.44 1.90 34.5 1.26 1.72

Tilled T2 29.4 1.30 1.47 12.0 1.18 0.06 15.8 0.94 0.79

53.3 2.66 53.3 2.67 46.B1

Burn B2

1.70 1.69 7 1.55 2.34

57.0 1.72 2.85 51.4 1.70 2.57 52.2 1.64 2.61

F1 40.1 1.55 2.00 27.5 1.28 1.38 48.2 1.67 2.41

Fallow F2 48.8 1.63 2.44 42.5 1.53 2.13 29.6 1.28 1.48

3.2il Phal Prties

3.2.1. Bulk Density (da) and Particle Size

Distribution

.69 to 1.14 g·cm–3.

The lowest value is in NT (0.69 g·cm–3). It increases

–3), F1

(1.14 (1.09 g·cm), and lesser in B1

n Tab le 2 (29.4%, 12.0% and 15.8%) and the

highest in B2 (57.0%, 51.4% and 52.2%), respectively

ting and the stirring

r pre-wetting (0.94 - 1.67 mm)

the st afterwettin9 - mm) tests. It

alwayrease NT - 2.6) to T72

- 2.42), T2 - 1.4), F1 - 2.m)

and F2 (1.48 - 2.44 mm), but increases in B1 (2.34 - 2.67

mm). The lowest MWD values

- 48.2%) and F2 (29.6% - 48.8%); but increases

In the Andosols from Mount Bambouto, the tillage

sults in a significant reduction of

the so

soil

. Soysicrope

The bulk density (da) varies from 0

significantly in T1 (0.93 g·cm–3), T2 (1.09 g·cm

g·cm–3) and F2–3

.77 g·cm–3) and B2 (0.79 g·cm–3). The silt (60 to 78%)

and clay (14 to 36%) fractions are dominant. The clay

fraction increases in T1 (36%) and T2 (31%), and de-

creases in B1 (20%) and B2 (14%) relative to NT (29%).

It also decreases in F1 (25%) and F2 (31%) compared to

T1 and T2. The highest fine silt content is in NT (53%).

It decreases in T1 (47%), B1 (34%), B2 (49%), F1 (45%)

and F2 (50%) and remains unchanged in T2 (53%). The

coarse silt abundance also decreases from NT (17%) to

T1 (13%) and T2 (13%), but increases in B1 (34%) and

B2 (29%). It also increases in F1 (28%) and F2 (16%)

compared to T1 and T2. The sand fraction is the less

abundant (2% to 12%) with the highest value in B1

(12%).

3.2.2. Aggregate Stability

The soil aggregate stability parameters are dis-

played i

after the slow wetting, the fast wet

ter pre-wetting tests.

The geometric mean diameter (GMD) of the soil

macro-aggregates decreases progressively after the slow

wetting (1.30 - 1.76 mm), the fast wetting (1.48 - 1.70

mm) and the stirring afte

sts. It decreases from NT (1.47 - 1.76 mm) to T1 (1.26 -

1.62 mm), T2 (0.94 - 1.30 mm), B1 (1.55 - 1.70 mm), B2

(1.64 - 1.72 mm), F1 (1.28 - 1.67 mm) and F2 (1.28 -

1.63 mm) whatever the test. The lowest GMD values are

in T2 (1.30 mm, 1.18 mm and 0.94 mm, respectively

after the slow wetting, the fast wetting and the stirring

after pre-wetting tests).

The mean weight diameter (MWD) of the soil macro-

aggregates also decreases severely after the slow wetting

(1.47 - 2.69 mm), the fast wetting (0.60 - 2.67 mm) and

mm) and B2 (2.57 - 2.85

irring pre-g (0.72.61

s decs from(1.919 mm1 (1.

mm(0.607 mm (1.3841 m

these soil macro-aggregates remain in T2 (1.47 mm,

0.60 mm and 0.79 mm after the slow wetting, the fast

wetting and the stirring after pre-wetting tests respec-

tively)

The water stable aggregates (WSA) abundance in the

study soils remains relatively high after the slow wetting

test, and vary from 29.4% to 57.0%. It decreases sig-

nificantly after the fast wetting (12.0% to 53.3%) and the

stirring after pre-wetting (15.8% to 52.2%) tests regard-

less of the land use and management systems. It de-

creases in T1 (34.5% - 48.4%), T2 (12.0% - 29.4%), F1

(27.5%

ightly in B1 (46.7% - 53.3%) and B2 (51.4% - 57.0%)

compared to NT (38.2% - 53.8%). The lowest WSA

abundance is in T2

4. DISCUSSION

Variations in most of the soil chemical and physical

properties are the key for understanding the impact of

land use and management systems on soil quality.

4.1. Changes in Soil Chemical Properties

management system re

il organic matter expressed by the soil OC (6.5% to

4.8%) and the total N (4.51% to 2.96‰) contents, giving

a reduction ratio of 26.1% and 34.4% respectively .

Similar reduction has been reported [9,10] with the

OC losses ranging from 15% to 40% within 2 - 12 yea

of tillage [11, 12]. Such reduction is commonly attribut

the microbial oxidation of the organic compounds

previously protected in the soil aggregates which where

destroyed by cultivation [13,14]. The burning manage-

ment system also reduces severely the soil organic matter

content by calcinations (OC: 6.5% to 0.8%, N: 4.51‰ to

0.95‰) giving a reduction ratio of 87.7% and 78.9%

respectively. Generally, reduction in the soil organic

P. Tematio et al . / Agricultural Science 2 (2011) 334-340

338

three land

en after 10years

oils

ent

ing to moderate rainfalls is

matter content influences negatively the fertility of An-

dosols, since it is known to play a central role in the ex-

changeable cations retention [15]. This reduction could

also increase the soil erodibility, causing an offsite

transport of the soil nutrients and the subsequent soil

fertility decline. Conversely, the fallow management

system improves the soil organic matter content relative

to the tillage management system (OC: 4.8% to 6.5%, N:

2.96‰ to 5.04‰) with an increasing ratio of 26.1% and

41.3% respectively. This increase in the soil organic

matter content with fallow may be consistent with addi-

tional supply of the organic residues which act as com-

post with time [16]. These particulate organic matters are

protected physically in soil aggregates [17].

In the Andosols from Mount Bambouto, the tillage and

burning management systems also lead to a net loss of the

CEC content (22.0 to 18.0 and 10.2 cmol·kg–1) with a

reduction ratio of 18.2% and 53.6% respectively, giving

rise to the soil fertility decline [18], whereas the fallow

management system restores it relative to the tillage

management system (18.0 to 21.6 cmol·kg–1) with an

increasing ratio of 16.7%. Inversely, the above

e and management systems are marked by a slight

increase of the sum of the exchangeable cations relative

to the natural cover (3.6 to 4.9 cmol·kg–1, 5.7 and 5.1

cmol·kg–1) with and increasing ratio of 26.5%, 36.8% and

29.4% respectively. In the tillage management system,

this may be due to an input of fertilizers during land

preparation. In the fallow management system, it sug-

gests that this unmanaged period can restore the soil

nutrients exported by the harvest of the plant biomass. In

the burning management system, it may be consistent

with the release of the base cations during soil calcination

[19] as indicated by the net increase in the soil pH values

in B1 (6.54) and B2 (6.18). Thus, the burning manage-

ment system improves the soil fertility through accumu-

lation of the exchangeable cations. But it is well known

that this improvement lasts only for a short period and

that the water erosion and the subsequent soil nutrients

leaching leads to soil impoverishment [19]. The soil

acidity also increases in the tillage management system

compared to the natural cover (pH 4.62 to 4.42), inducing

the decrease in the agricultural productivity [20]. Even 10

years of the fallow management system practice (F2 plots)

is not enough to improve this strong acidity induced by

the tillage management system. Always in the Andosols

from Mount Bambouto, the long-term tillage (T2 plots)

and the fallow management systems have brought the

cations equilibrium close to the optimal equilibrium (T2:

73/20/7, F1: 78/17/5 and F2: 63/33/4) and consequently

improve Andosol fertility. Inversely, the short-term till-

age (T1 plots) and the burning management systems

provoke the cations imbalance (T1: 54/39/7, B1: 58/25/17

and B2: 41/51/8) with a significant Ca2+ deficiency. This

Ca2+ deficiency may induce a severe antagonism between

the cations during the plants nutrition.

4.2. Changes in Soil Physical Properties

The soil compaction (36.7%) induced by the tillage

management system and expressed by the soil bulk den-

sity increase (0.69 to 1.09 g·cm–3) has significant effect

on soil physical properties. It reduces infiltration and

percolation of water, and thus favours the surface runoff

and land degradation by soil erosion. Ev

of the fallow management system practice, these s

seem to have not recovered from the tillage managem

stem induced compaction.

The water stable aggregates (WSA: 12.0% - 53.3% and

15.8% - 52.2%) abundance, the geometric mean diameter

(GMD: 1.18 - 1.70 mm and 0.94 - 1.67 mm) and the mean

weight diameter (MWD: 0.60 - 2.57 mm and 0.79 - 2.61

mm) values reveal that the fast wetting and the stirring

after pre-wetting tests representing moderate to violent

storms highly disrupt the Andosol macro-aggregates. The

slow wetting test correspond

ast disruptive (WSA: 29.4% - 57.0%; GMD: 1.30 - 1.76

mm; MWD: 1.47 - 2.85 mm). Globally, the Andosols

from Mount Bambouto have low to moderate resistance

to water erosion. As the land use and management system

is concerned, the tillage management system lead to an

important destruction of the Andosol macro-aggregates

(WSA: 12.0% - 48.4%; GMD: 0.94 - 1.62 mm and MWD:

0.60 - 2.42 mm), whereas the burning management sys-

tem regenerates them ((WSA: 46.7% - 57.0%; GMD: 1.55

- 1.72 mm and MWD: 2.34 - 2.85 mm). The fallow man-

agement system also regenerates the Andosol macro-

aggregates after the tillage management system practice

(WSA: 27.5% - 48.8%; GMD: 1.28 - 1.67 mm and MWD:

1.38 - 2.44 mm). The destruction of the Andosol macro-

aggregates by the tillage management system with it

subsequent increasing clay fraction (36%) may be con-

sistent with the mechanical breakdown of the soil ag-

gregates by ploughing. The regeneration of the Andosol

macro-aggregates with the burning management system

practice may be related to Al3+ activity in the soil solution.

In fact, above pH 5.5, Al3+ precipitates in soil as hy-

droxides and can act as links between mineral particles,

generating soil aggregates. Under the fallow management

system, the regeneration of the Andosol macro-aggre-

gates may be associated to the formation of the organo-

metal and oxides-humus complexes with organic acids

acting as binding agent [21]. The increase in the Andosol

macro-aggregates abundance in both cases and the rela-

tively low bulk density indicate well-structured soils with

good pore connectivity.

P. Tematio et al . / Agricultural Science 2 (2011) 334-340

339339

exchangeable cations and t

the optimal equilibrium after

are not enough to restore ef-

fic

rovement lasts only for a

5. CONCLUSIONS

The tillage management system is a significant driver

of the Andosol fertility decline. It reduces significantly

the soil organic matter and the CEC content, increases

soil acidity and compaction, and destroys the Andosol

macro-aggregates; the chemical and physical properties

that affect negatively the Andosol quality. The relative

increase of the sum of thehe

cations equilibrium close to

10 years of tillage practice

iently the Andosol fertility.

The burning management system has mitigated influ-

ences on Andosols quality. The severe reduction of the

soil organic matter and the CEC content, and the cations

equilibrium imbalance in the burning management sys-

tem affect negatively the Andosol quality. Inversely, the

net increase of the sum of the exchangeable cations and

the soil pH above 6, and the fairly high soil macro-ag-

gregates abundance contribute to improve significantly

the Andosol quality. But this imp

ort period because the water erosion and it subsequent

nutrients leaching leads to the soil impoverishment.

The fallow management system globally improves

significantly the Andosol quality. It is sustainable in term

of the soil organic matter, the CEC and the sum of the

exchangeable cations increase, and the soil macro-ag-

gregates regeneration after the tillage management sys-

tem practice. But, even 10 years of the fallow manage-

ment system is not enough to regenerate efficiently the

soil macro-aggregates and improve the soil acidity.

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